Electromagnetic device



Jan. 24, 1939. I M, BERGES 2,145,021

ELECTROMAGNETIC DEVICE Filed Se t 5, 1955 INVENTOR.

A TTORN'Ei M Patented Jan. 24, 1939 UNITED STATES PATENT OFFICEELECTROMAGNETIC DEVICE Application September 5, 1935, Serial No. 39,345

2 Claims.

This invention relates to electromagnetic devices, and particularly toelectromagnetic devices of the type wherein reversal of current causes acorresponding reversal in the direction of force application, and hencea reversal of movement of a part, such as a valve, lever, switchelement, or servo-motor, actuated thereby.

An object of the invention is to provide novel means for controlling theflow of current to an electromagnetic device of the indicated character.

A second object is to provide light sensitive control of the currentflow.

A third object is to provide, in combination with an electromagneticelement and a light sensitive device, such as a photo-electric cell, asys tem of electrical circuits and devices connecting said cell withsaid electromagnetic element in such a manner as to achieve the abovementioned objectives.

These and other objects of the invention will become apparent frominspection of the following specification when read with reference tothe accompanying drawing wherein is illustrated the preferred embodimentof the invention. It is to be expressly understood, however, that thedrawing is for the purpose of illustration only, and is not designed asdefinition of the limits of the invention, reference being had to theappended claims for this purpose.

In the drawing, reference character 6 designates a coil which may bepart of a magnet, relay, motor, etc.; and, l designates a thermionicvacuum tube, 8 a photo-cell, and 9, i3 and I6 are resistors.

The fixed grid bias of vacuum tube 1 is initially adjusted so that theplate current of the vacuum tube is small enough to allow the necessaryrelay operating current to flow from resistor 9, through coil 6 andthrough resistors I31), l 30, and l3d of the voltage divider l3. When asmall amount of light is allowed to fall on the photo-cell the cell willpass current through itself and resistor 15, causing a voltage drop inIS and decreasing the grid bias of vacuum tube 1. As the grid bias isdecreased the plate current will increase causing more voltage drop in9. As the amount of light is increased the voltage drop in 9 will alsoincrease until a point is reached where the voltage drop in 9 is exactlythe same as that in I 3a. When this occurs there will be no current fiowin coil 6 and it will be in its neutral position.

If the amount of light on the photo-cell is still further increased thevoltage drop in 9 will become greater than that in I 3a and the currentwill flow in relay 6, but in a direction opposite to the first.described direction of flow. (Current through 9 plus current through 6being the total plate current of vacuum tube 1.)

An example of a use to which the above invention may be applied is asfollows:

Suppose an instrument to be so arranged that light from a light sourceplaced behind it can pass through an aperture in the instrument face andfall on the photo-cell. Now suppose the 10 instrument to be equippedwith a movable index element adapted to assume any one of threepositions, such that in the first position maximum light will act uponthe photo-cell, in the second position a moderate amount of light willfall on the cell, and in the third position'all light from the lightsource will be excluded.

Let position 2 be the normal position of the index element. When in thisnormal position, let it be assumed that the grid bias, light intensity,etc., will be so adjusted that the voltage drop in 9 and l3a are equal.If so, no current will flow in relay 6. Now should the index elementmove to position I, the increase in light falling on the photo-cell willcause the relay 6 to operate in one direction; and should the pointermove to position 3, the decrease in the amount of light falling on thephoto-cell will cause the relay 6 to operate in the opposite direction.

The foregoing is merely a suggestion of one field of utility for theelement 6. Other uses will be obvious, in the light of the explanationset forth in the introductory paragraphs of this specification.Likewise, possible variations in the circuit arrangement (such as thesubstitution of other current consuming elements for the resistors l3)will be obvious, and are embraced in the appended claims.

What I claim is:

1. The combination with a photo-electric cell and a thermionic devicehaving a grid element,

a resistor having at least three sections (I31), I30, 13d) two of which(I31), I30) are in shunt relationship to the thermionic device, and athird section in series relationship thereto, a source of electricalenergy for the photo-electric cell, means exclusive of said energysource for electrically connecting one electrode of said photocell withsaid resistance element, at a point between the two first-named sectionsthereof, means electrically connecting the other electrode of saidphoto-cell with said grid element, electromagnetic means interposed inthe circuit between said thermionic device and said resistor, and meanscooperating with said electromagnetic means to reverse the direction ofcurrent flow through said electromagnetic means in response tovariations in the grid potential of said thermionic device.

2. The combination with a photo-electric cell and a thermionic devicehaving a grid element,

a resistor including a series of resistance elements 1 in Wheatstonebridge association with said thermionic device, a source of energy forthe photoelectric cell, means exclusive of the source of energy forelectrically connecting one electrode of said photo-cell with saidresistance elements,

means electrically connecting the other electrode of said photo-cellwith said grid element, electromagnetic means interposed in the circuitbetween said thermionic device and said resistor, and

means alternating between a shunt and series relationship to saidelectromagnetic means to correspondingly alternate the direction ofcurrent flow through said electromagnetic means in response tovariations in the grid potential of said thermionic device.

' DONALD M. BERGES.

